Conventionally, a communication protocol of Controller Area Network (CAN) has widely been employed in communication among multiple electronic control units (ECUs) mounted in a vehicle. A communication system with the CAN communication protocol is so configured that multiple ECUs are connected to a common CAN bus, and transmission/reception of messages are performed by an ECU at the reception side obtaining a signal output to the CAN bus by an ECU at the transmission side.
Furthermore, in the case where multiple ECUs simultaneously transmit messages which then collide against each other on the CAN bus, adjustment (arbitration) processing is carried out between communication devices based on CAN-IDs attached to the messages. Due to the arbitration processing, a message with a CAN-ID of a high priority is transmitted first and therefore the transmission of the message with a CAN-ID of a low priority is delayed. Since the arbitration processing may cause a delay of a message, the ECU that received the message cannot know the time when this message was generated (or the time when the message was tried to be transmitted first).
Japanese Patent Application Laid-Open Publication No. 2006-316739 proposes a distributed control system configured to transmit a time synchronization message for instructing that an actuator driving electronic control device obtains sensor information of an inlet valve stroke sensor while an engine controlling electronic control device obtains sensor information from an inlet throttle sensor at the same timing, the actuator driving electronic control device obtaining sensor information of an inlet valve stroke sensor based on the timing instructed by the time synchronization message and transmitting the obtained sensor information to the engine controlling electronic control device together with the time of obtainment.